Published by Australian Academy of Science
Glossary | Predicting natural events

anthropogenic. Caused or induced by humans; of human origin.

catchment. The area from which a river, stream, lake or other body of water receives its water.

complex system. A complex system is one in which there are multiple interactions between many components. The properties of a complex system are not completely explained by an understanding of its component parts.

erosion. A term that can be applied to soil or rock. Soil erosion is the gradual loss of any type of soil from the soil surface, usually caused by water and wind. Rock is eroded when it is slowly made smoother or worn down, again by wind or water.

global warming. An increase in the average temperature of the Earth's surface. Global warming is one of the consequences of the enhanced greenhouse effect and will cause worldwide changes to climate patterns.

hydrology. The study of water, its properties and movement through the Earth's land and atmosphere. Hydrology includes the study of the distribution of water, the accumulation of water – in lakes, oceans and underground – and the effects of water on the earth's surface.

model. Solving complex problems associated with real situations is often made easier by setting up a model of the situation – a mathematical description of the problem. To set up a model, a problem is simplified and only those aspects that can be represented mathematically are included.

After the problem is solved mathematically, tentative solutions are translated back to the real situation, as possible real solutions. At this stage the inadequacy of the simple model may be revealed, and some parts of the process may need to be changed. More information on models and modelling can be found at What is modelling? (Nova: Science in the news, Australian Academy of Science).

threshold. The point at which a signal can be detected or is strong enough to trigger a change.

water (hydrological) cycle. A biogeochemical cycle through which the Earth's fixed supply of water is collected, purified and redistributed from the environment to living organisms and back to the environment. The water cycle is powered by the sun causing evaporation into the atmosphere of water from plants and from the Earth's surface.